From: Andi Kleen <andi@firstfloor.org>
To: Shaohua Li <shaohua.li@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>,
        lkml <linux-kernel@vger.kernel.org>, Rik van Riel <riel@redhat.com>,
        Hugh Dickins <hughd@google.com>
Subject: Re: [PATCH]mmap: avoid unnecessary anon_vma lock
References: <1301277532.3981.25.camel@sli10-conroe>
Date: Mon, 28 Mar 2011 09:57:39 -0700
In-Reply-To: <1301277532.3981.25.camel@sli10-conroe> (Shaohua Li's message of
	"Mon, 28 Mar 2011 09:58:52 +0800")
Message-ID: <m2fwq718u4.fsf@firstfloor.org>
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Shaohua Li <shaohua.li@intel.com> writes:

> If we only change vma->vm_end, we can avoid taking anon_vma lock even 'insert'
> isn't NULL, which is the case of split_vma.
> From my understanding, we need the lock before because rmap must get the
> 'insert' VMA when we adjust old VMA's vm_end (the 'insert' VMA is linked to
> anon_vma list in __insert_vm_struct before).
> But now this isn't true any more. The 'insert' VMA is already linked to
> anon_vma list in __split_vma(with anon_vma_clone()) instead of
> __insert_vm_struct. There is no race rmap can't get required VMAs.
> So the anon_vma lock is unnecessary, and this can reduce one locking in brk
> case and improve scalability.

Looks good to me.
-Andi

-- 
ak@linux.intel.com -- Speaking for myself only
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